1. Field of the Invention
This invention relates to a logic circuit, more particularly to a logic circuit with a low leakage current.
2. Description of the Related Art
Referring to FIG. 1, a conventional three-input complementary metal-oxide-semiconductor (CMOS) AND logic circuit 1 includes a NAND logic gate 11 which is adapted to perform a NAND operation on three input signals (A, B, C) so as to generate a control signal ( ABC), and an inverting logic gate 12 which is adapted to perform an inversion operation on the control signal ( ABC) so as to generate an output signal (ABC) that is representative of an AND operation of the input signals (A, B, C).
The NAND logic gate 11 includes three series-connected n-type metal-oxide-semiconductor field-effect transistors (NMOS transistors) 111, 112, 113 adapted to be coupled between a low voltage source 21 and three parallel-connected p-type metal-oxide-semiconductor field-effect transistors (PMOS transistors) 114,115,116. The parallel-connected PMOS transistors 114, 115, 116 are adapted to be coupled between a high voltage source 22 and the series-connected NMOS transistors 1111, 112, 113. A node of connection between the series-connected NMOS transistors 111, 112, 113 and the parallel-connected PMOS transistors 114, 115, 116 serves as an output terminal of the NAND logic gate 11. The inverting logic gate 12 includes an NMOS transistor 121 and a PMOS transistor 122 that are connected in series between the low and high voltage sources 21, 22. Gate terminals of the NMOS and PMOS transistors 121, 122 are coupled to the output terminal of the NAND logic gate 11. A node of connection between the NMOS and PMOS transistors 121, 122 serves as an output terminal of the conventional three-input CMOS AND logic circuit 1.
As dimensions of CMOS devices continue to scale down, the problem of leakage current in conventional CMOS logic circuits, such as the aforesaid conventional three-input CMOS AND logic circuit 1, gets worse. Hence, there is a need to design a logic circuit that has a relatively lower leakage current, while performing the same function as the conventional logic circuit.